THEORY OF OPERATION - CONTINUED
HYDRAULIC SYSTEM - CONTINUED
When the auxiliary circuit is the only hydraulic circuit in operation, the auxiliary circuit will have the highest sig-
nal oil pressure in the hydraulic system. When the hydraulic oil exits port (5), pilot oil enters the control valve
through port (11). The pilot oil flows through the shock reducing check valve (12). The shock reducing check
valve moves to the left.
Pilot oil flows into chamber (10). As the pilot oil moves spool (25) to the left, spring (24) is compressed. When the
spool moves to the left, pump supply oil flows from passage (15) over the metering slots in the spool into passage
The hydraulic oil in passage (16) flows to the pressure compensator valve (6) and passage (26). In the pressure
compensator valve, the hydraulic oil flows into internal passages. The pressure compensator valve moves up. As
the pressure compensator valve moves up, the cross-drilled passage is opened to passage (4). Some of the hydrau-
lic oil flows around the pressure compensator valve to spring (3). The hydraulic oil that flows to spring and pas-
sage (4) is signal oil. Spring and the signal oil balance the pressure compensator valve against the hydraulic oil
pressure in passage (16). This controls the flow across spool (25).
The signal oil in passage (4) flows to the pressure compensator valve in each control valve. The signal oil also
flows to the pressure and flow compensator valve on the hydraulic pump. The signal oil controls the output of the
hydraulic pump. The hydraulic pump upstrokes and the hydraulic oil pressure in passage (16) increases. When the
hydraulic oil pressure in passage raises above circuit pressure, the hydraulic oil unseats load check valve (19) and
flows to passages (14 and 17).
In passage (17), the spool blocks the flow of the hydraulic oil. In passage (14), the hydraulic oil flows around spool
(25) to passage (13). Then, the hydraulic oil flows through port (5) to the work tool.
Hydraulic oil from the work tool flows to port (2). Then, the hydraulic oil flows to passage (18) around spool (25)
to tank passage (20). Then, the hydraulic oil flows to the tank.
When the operator releases the pilot valve, the flow of pilot oil to the pilot valve moves the shock reducing check
valve to the right. The hydraulic oil flows through an orifice. This dampens the flow of hydraulic oil to the pilot
valve. The spool slowly closes off the hydraulic oil to the circuit. Spring (24) moves spool (25) to the HOLD posi-
tion. Load check valve (19) blocks hydraulic oil in the hydraulic lines.
The flow of hydraulic oil through the control valve is adjustable. Remove cap (A). Loosen nut (B). Turn screw (C)
clockwise in order to decrease the flow of hydraulic oil through the valve. Turn screw counterclockwise in order to
increase the flow of hydraulic oil through the valve. Tighten nut. Install cap.